Compensating for microphone frequency response in FFT

On Jul 14, 1:10&#4294967295;am, Les Cargill <lcargil...@comcast.com> wrote:
> Tyler Mandry wrote:
> > On Jul 11, 1:43 am, Les Cargill<lcargil...@comcast.com> &#4294967295;wrote:
> >> Tyler Mandry wrote:
> >>> I'm making an application that displays an FFT of sound data from a
> >>> microphone. One thing I need to be able to support is calibrating to
> >>> the frequency response of the microphone, which will be given to the
> >>> program via a calibration file. The calibration file contains + or -
> >>> dB values for different frequencies, like this:http://pastebin.com/raw.php?i=wFBwZaTS
> >>> . I can just apply the calibration after the FFT and before displaying
> >>> it on the screen.
>
> >>> My problem is this: how should I interpolate between those values,
> >>> which are essentially just select points of the whole frequency
> >>> response of the microphone? A naive approach might be to define rigid
> >>> rectangular bands around those points and, for each frequency in an
> >>> FFT, pick one or another calibration line to apply to that frequency.
> >>> This would cause visible jumps in the FFT graph, however. Another
> >>> solution might be to use linear interpolation, but I'm still not sure
> >>> that's the best way.
>
> >>> Is there a "standard" way to do this, that programs like Smaart or FFT
> >>> devices do? What would be the best way to generate a continuous curve
> >>> from those few fixed points?
>
> >> You can spline it.
>
> >> If the dataset just proves to be completely inadequate, you can make a
> >> spark gap generator from an old strobe flash unit, some sort of spark
> >> gap and an inductive loop pickup. Deconvolve the mic's read of the
> >> impulse against the loop pickup's read of it. That produces a
> >> convolution signature from which a response curve can be derived.
>
> >> Voxengo makes a good deconvolver.
>
> >> --
> >> Les Cargill
>
> > I hadn't thought about using splines, that may be the best option.
>
> > And while that was -very- good and interesting information on how to
> > measure the impulse response of a microphone, it doesn't do me much
> > good, as it's the end user of my application that will be providing
> > both the microphone and calibration, and I don't think I will be
> > telling them to take apart a strobe lamp in the help/how-to :). Thanks
> > though, I might be able to use that someday!
>
> That might be a small service sub-business to go with the app... most
> might be perfectly happy with the 12-point cal, but some might not...
>
> --
> Les Cargill

What kind of service do you mean?
I think I will be allowing as many points as the user wants.